Compare lactulose vs. Metamucil

Head-to-head comparisons of medication uses, side effects, ratings, and more.

Generlac (lactulose)

Prescription only

Metamucil (Psyllium)

Relieves constipation and gets rid of ammonia in people with liver problems.

Generlac (lactulose) relieves constipation and high ammonia levels, but it can take up to 48 hours to work.

Helps get things moving.

The natural psyllium fiber in Metamucil (Psyllium) does more than relieve constipation. It lowers cholesterol, keeps blood sugar levels healthy, and makes you feel less hungry between meals.

5.2/ 7 average rating with 454 reviewsforMetamucil
  • Generlac (lactulose) is the first-choice treatment for brain conditions caused by high ammonia levels.
  • Can be used if you have severe chronic constipation leading to blockage.
  • Available in generic.
  • Can be taken orally or rectally.
  • Psyllium is the most recommended brand of natural fiber laxative
  • Some people feel that taking Psyllium is a hassle, but most think it's worth it.
  • It has multiple health benefits, good to control your hunger between meals, improves your blood sugar and lowers cholesterol levels.
  • Studies show it works better than a stool softener for constipation.
  • Should not be used if you are on a galactose-restricted diet.
  • Does not provide rapid relief of constipation. Talk to your doctor or pharmacist if you need quick relief.
  • Generlac (lactulose) has a very sweet flavor that most people don't like.
  • You may have to take Psyllium daily for 1-3 days to see full effects.
  • If you don't take it with enough liquid, it could swell, block your throat and cause choking.
  • Not the best choice for people who have swallowing problems or aren't able to drink lots of liquids.
  • Psyllium contains psyllium. Don't take if you have an allergy to psyllium from breathing it in or swallowing it.
  • Can cause gas and mild belly cramps.
Used for
Dosage forms
  • Liquid
  • Powder
  • Liquid
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Side effects
The Generlac (lactulose) FDA package insert doesn’t have numbers about how common side effects are.
The Metamucil (Psyllium) FDA package insert doesn’t have numbers about how common side effects are.
Risks and warnings
  • Mineral imbalances

    Taking Generlac (lactulose) for more than 6 months

    ...and 3 more risk factors

  • Increased blood sugar


See more detailed risks and warnings
  • Bowel blockage

    Age 60 or older

    ...and 3 more risk factors

  • Serious allergic reaction

    Sensitivity to psyllium

See more detailed risks and warnings